Although the panels or coatings made from solid wood or wood derivatives have a high bending strength, such as in the case of plywood, medium density fiberboards (MDF) or particle boards (OSB), they also have a low performance in terms of water resistance, dimensional stability, in addition to high susceptibility to attacks from fungi, insects and microorganisms, as well as low performance in what concerns its reaction to fire (in most cases with a classification equivalent to euroclass D).
The currently existing cement wood panels, which are commercially referred to as “VIROC”, offer some advantages when compared to the aforementioned ones, since the mechanical performance and durability were already guaranteed by the presence of Portland cement in their composition. However, their classification as regards the fire action does not allow the degree of incombustibility to be achieved, being generally rated with no more than Class B.
On the other side, the U.S. Pat. No. 6,221,521 B1 discloses a process wherein semi-hydrated or anhydrous gypsum is used and reinforced with organic fibers containing additives such as potassium sulphate, in order to provide multilayer panels, and which is classified as incombustible according to ASTM E 136.
The U.S. Pat. No. 5,320,677 discloses another process wherein a mixture of fluidized gypsum with cellulose fibers is heated under pressure, being then subject to cooling in order to produce a panel with the desired conformation, although with a reference to gypsum calcination.
The U.S. Pat. No. 5,342,566 is in line with the previous ones, however it comprises the use of light-weight fillers, such as perlite, combined with gypsum and cellulose fibers, for the production of multilayer panels. In the U.S. Pat. No. 5,135,805, the possibility to use fibers of different origins is mentioned, such as glass or another mineral, and/or polypropylene in percentages ranging from 10 to 20%. All of these panels are considered incombustible according to ASTM E 136, but their formula does not contain cement and that is the reason why they have a limited scope of application, particularly in what concerns demands of a structural nature and exposure to outer environment.